We come now to the third and last method employed in transmission, which consists in sending a rapidly vibrating current over the line, which is made to set a telephonic dia phragin in vibration.
The source of the vibratory current is the small dynamo shown at d. From the arrange ment of circuits, it will be seen that the comintator, B, cuts the line coils of the vibratory magneto, that is. the outer ring of magnets, out of circuit, except at the instant of passage of the poles, and thus reduces the resistance of the circuit from 160 to ri ohms, which changes evidently occur in continuous rapid succession, sending a vibratory current over the line. These currents charge the condenser, C", at the distant station, which tends to increase their abruptness, and thence pass into the vibratory re ceiver or relay . The latter is shown in detail in Fig. 10. It consists of a horseshoe magnet, .31, upon which aro mounted the coils, I', through which the vibratory currents from the line are made to pass. Opposite the poles of the magnet is placed the diaphragm, li, which has a platinum pin, C, mounted on its center. Besting upon this pin is an other, B, which is attached to the end of a lever, which, together with the diaphragm, 1), is in circuit with a sounder, A local battery is here shown in circuit merely for the sake of clearness, the current being in reality taken from the local leads of the dynamo.
Now, when the key, is open, the armature of the transmitter, 3 is on back stop, and closes a circuit in cluding, a resistance, so that the current from the vibratory generator is short: circuited and does not go out over the line. When the key, h7, is depressed, 'however, the armat are of 3 is attracted, breaks the short circuit, and the vibratory currents then pass out to the line. Arriving at the receiver, shown at Fig. 8, they set the diaphragm, 1), itr rapid vibration, so that the pins. B and C, are given a rapid make-and-break motion ; in fact, so rapid is the motion and so short a time arc the pins in contact, that the local circuit is practically open, and the sounder has not time to act, being purposely made sluggish in its movements ; the local circuit remains open. then, as long as the key, is depressed. The dots and dashes of the key are therefore received on the vibratory receiver as a series of buzzes," which are transformed in the manner described into dots and dashes on the local sounder, S. Both the relays as well as the vibratory receiver are wound differentially, as in
the ordinary duplex service.
The Edison. Phonoplex.—The ordinary duplexing of a wire, which increases facilities between terminal points only, has been largely applied, but until Mr. Thomas A. Edison devised this new method of transmission no means were available by which the capacity of intermediate offices on a single Morse circuit could be increased. Through the use of the phonoplex system extra circuits arc provided, by means of which snore than double the amount of service may be derived from a single wire than is at present obtained, while its extreme sim plicity of detail and adjustment places it within the easy control of ordinary operators.
The principle upon which the system is operated is induction.
The instruments employed for respond only to in duced currents thrown upon the line by transmitting devioes, which currents interfere in no way with Morse instruments in the same circuit, being made to pass around them through con densers, while Morse waves in turn have no perceptible effect upon the phonoplex apparatus ; thus, two or more independent circuits may be provided on a. single wire, as will be more fully explained hereafter.
The apparatus for the equipment of an office consists of a key, transmitter, magnetic coil, small resistance box, and the phone, which last responds to incoming signals, two condensers, battery ; and the whole is arranged to occupy no more space than ordinary Morse instruments. Fig. 11 represents the phone. A hollow column of brass resting upon a wooden base encloses the magnets. At the lower end is a rack and pinion by which these can be adjusted with reference to the diaphragm. To the center of the latter there is attached a pin with thumb-nut and binder at the top, and encircling the pin loosely is a split-hardened steel ring which rests upon the dia phragm. When the latter is snapped by the attraction of the momentary current in the mag net, it throws the ring violently against the stop nuts and produces a sharp, loud click, The steel ring has a pin projecting from its side that passes between two prongs, which, while permitting free up and down motion, prevents the ring from turning and altering the sound. Over the top of the phone there is clamped a thin brass plate as a protection for the projecting screw.